Need info on M16A4 complete uppers by Colt/FN. Any difference between the two? One better than the other?

The short answer is no. There may be some different values assigned because of perceived collectibility, but actual A4 uppers from both companies should be similar quality in barrel, construct of carrier group, etc.

I agree with Kevbo

I was issued both by Uncle Sam, and they performed flawlessly.

I was issued an FN M16A4 in basic training with a adjustable stock. I loved it and I shot great with it.

If I was in the market for one, I would buy the FN just because it was the last ones I used.

For years I carried an M16A4 and never had a lick of problems, that were not induced by me.

In fact I have always favored an M16A4 variant over the M4.

The TDP is pretty delineated. I would be surprised if there was any true difference between the two. One upper to the next, maybe QC type issues, but over the thousands of them out there, they should all be the same.